Heater runs but spa overheats beyond the set temperature

Safety: Turn off power and gas if water temperature exceeds safe levels. Do not allow bathers in overheated water.

• Verify setpoint: Confirm the spa set temperature on the SunHeater and any external controller.
• Check sensor accuracy: Compare displayed spa temperature to an independent thermometer. If the display is much lower than actual, the Spa Temperature Sensor may be faulty.
• Inspect external control wiring: If using automation, ensure that the heater is not being held in a constant call-for-heat state by a stuck relay or miswired contact.
• Test in stand-alone mode: Temporarily disconnect external controls and operate the heater only from its local panel. If overheating stops, the issue is in the external system.
• Replace control board if needed: If the heater continues firing past the setpoint with correct sensor readings, the main control board's relay may be stuck and should be replaced.